Studies are being conducted on the properties of leukemia-specific antigens on AKR spontaneous leukemia (KSL) cells. Nonvirus-associated leukemia-specific surface antigens, consisting of the common and the individual antigens, are being demonstrated by indirect immunofluorescent microscopy. As part of a wide scope of research, studies are being made on the incidence and properties of naturally occurring antibodies against the primate type C virus in sera from human individuals. Immunological and virological methods are being used in the screening.